The present invention relates to a plastic optical fiber excellent in heat resistance and a process for the production of the same.
Recently, plastic optical fibers have been noticed owing to their features such as excellent flexibility and processability, large numerical aperture and so on, so that the demand for them has been remarkably increased. However, these plastic optical fibers are insufficient in heat resistance, because, for example, an optical fiber containing a core made of polymethyl methacrylate is resistant only to a temperature up to 85.degree. C. and an optical fiber containing a core made of polycarbonate is resistant only to a temperature of 125.degree. C. at the highest, so that they are unsatisfactory for use in the vicinity of an automotive engine, though such use is one of the fields of short-distance communication which will have a great demand for optical fibers. For example, a plastic optical fiber having a sheath made of a polymer mainly comprising .alpha.-fluoroacrylate as disclosed in Japanese Patent Kokai Publication No. 61-103107 is substantially resistant only to a temperature up to about 120.degree. C., because the glass transition point of the polymer constituting the sheath is about 120.degree. C. Further, a plastic optical fiber having a sheath made of a polymer component mainly comprising poly-4-methyl-pentyne as disclosed in Japanese Patent Kokai Publication No. 61-245110 has serious defects in practical use because the polymer constituting the sheath discolors in the long-term heat resistance test at 125.degree. C. which lowers the light transmission performance and because the adhesion of the sheath to the core is poor, though it has a melting point of 240.degree. C. to be satisfactory in respect of heat distortion resistance.